1. Field of the Invention
The invention relates to a vehicle powertrain having an internal combustion engine with an engine oil lubrication pump powered by an electric motor.
2. Background Art
A hybrid electric vehicle powertrain typically has two electric machines and an internal combustion engine. In one operating mode, the engine and the electric machines define two power flow paths to vehicle traction wheels. One electric machine functions as a generator in one operating and as a motor in another operating mode. Likewise, the other electric machine operates as a motor or as a generator depending upon the operating mode. The electric machines are electrically coupled to a high voltage traction battery.
In a so-called divided power hybrid electric vehicle powertrain, a first power source is established as the engine output power is divided into two paths by controlling the first electric machine, which in this instance would be functioning as a generator. A mechanical power flow path extends from the engine through a gear system to a gearing arrangement, which delivers driving power to the traction wheels of the vehicle. An electrical power flow path extends from the engine to the generator and to the second electric machine, which in this instance would function as a motor. The output torque of the motor is delivered to the traction wheels through the gearing. The engine power is divided by controlling generator speed to effect a so-called positive power split. If the generator functions as a motor, power input to the gearing from the generator will establish a so-called negative power split. The generator in this powertrain configuration can be braked so that the engine can deliver torque through a solely mechanical path as an electric power flow path is established by the motor, which is powered by the battery.
When the powertrain is configured to provide a second power source, the motor alone, using battery power, can provide driving torque to the traction wheels independently of the engine for both forward and reverse operation of the vehicle. The generator alone acting as a motor can propel the vehicle forward using battery power with the engine off.
It is apparent from the foregoing description that the engine must be started or stopped each time the powertrain transitions from one operating mode to another.
The engine, as in the case of conventional powertrain systems, requires a lubrication oil pump, which typically is driven by the engine as lubricating oil is circulated from an engine oil sump through moving components of the engine. It then is drained back to a sump. The oil sump in this configuration is referred to as a wet sump.
An example of an engine with a wet sump may be seen by referring to U.S. Pat. No. 5,606,946 (FIG. 7a). If the engine is provided with a so-called dry sump, the engine driven oil pump must transfer lubricating oil rapidly through the engine from an auxiliary oil reservoir. Such a lubricating oil flow circuit is illustrated, for example, in FIG. 7b of U.S. Pat. No. 5,606,946.
In a hybrid electric vehicle of the type described above, frequent engine stops and starts will reduce fuel consumption, but before each start there is a low oil pressure in the lubrication system. The frequent engine start/stop cycles can increase engine wear due to thin oil films on surfaces between relatively movable elements of the engine, which potentially affects adversely engine life. In a typical hybrid electric vehicle powertrain, the unique duty cycles for the electric machines can vary based on environmental and engine usage profiles. It also is difficult to detect when an oil change in the engine should be made for routine engine maintenance.